Method of treating filamentous articles of ethylene polymer and the resulting product



Apnl 23, 1963 J. E. PRITCHARD 3,

METHOD OF TREATING FILAMENTOUS ARTICLES 0? ETHYLENE POLYMER AND THE RESULTING PRODUCT Filed Oct. 23, 1959 DRAWING QUENCHJ INVENTOR. J.E PRITCHARD A T TORNE VS United States Patent Ofiice 3,086,275 Patented Apr. 23, 1963 3,086,275 METHOD OF TREATING FILAMENTOUS ARTI- CLES 01" ETHYLENE POLYMER AND THE RE- SULTING PRODUCT James E. Pritchard, Bartiesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Oct. 23, 1959, Ser. No. 848,310 11 Claims. (Cl. 28-76) This invention relates to a method of improving the surface properties of filamentous articles such as thread, rope, Cordage and monofilaments formed from ethyiene polymers. in another aspect the invention relates to filamentous articles which have been treated according to the discovered method. In still another aspect this invention relates to textile materials formed from such filaments.

Fibers formed from ethylene polymers of high density have excellent tensile properties, chemical resistance and durability. Textiles woven from such fibers have been used to manufacture filter cloths, seat covers for automobiles, curtains and the like. The smooth hard surfaces of these fibers, however, have a low coefficient of friction and for this reason dimensional stability of fabrics woven from these fibers leaves room for improvement. One expedient which has been used to effect improvements in dimensional stability is to subject the fabric to calendering whereby the textile is converted to a unitary structure. Textiles treated in this manner, however, possess poor hand and other physical limitations making them unsatisfactory for certain applications.

I have discovered that the surface properties of filamentous articles of ethylene polymers can be significantly altered to increase the coefficient of friction thereof by immersing the article in a liquid hydrocarbon solvent at 100 to 125 C. and withdrawing the article from the solvent after a residence time of 0.05 to seconds. In addition to increasing the coefficient of friction on the surface of these filaments, the appearance of the article is enhanced by reducing the high gloss to a soft attractive luster. Fibers thus treated can be woven into fabrics having enhanced dimensional stability, good hand and better eye appeal.

It is an object of my invention to provide a method of treating filamentous articles of ethylene polymers to increase their surface coeificient of friction.

it is another object of my invention to provide a method of treating fibers of ethylene polymers to improve their suitability for textile manufacture.

Still another object is to provide an improved filamentous article of ethylene polymer having increased surface coefficient of friction. Fibers, monofilarnents or threads are more suitable for weaving into fabrics while rope and cordage have improved knotting properties.

Another object is to provide a fabric woven from ethylene polymer fibers treated to modify their surfaces.

Other objects, advantages and features will be apparent to those skilled in the art from the following discussion and drawing which shows schematically my invention in a fiber drawing process.

The polymers which are used to form the filamentous articles treated according to my invention are ethylene polymers of high density, that is, having a density in the range of 0.940 to 1.00 at 25 C. These polymers include polyethylene and also copolymers of ethylene with monoolefins having 3 to 4 carbon atoms per molecule, i.e. proplyene, l-butene or Z-butene. In order for the c-opolymer to fall in the desired density range the monomer system from which the copolymer is polymerized should not contain over 30 weight percent propylene or butene and preferably not over weight percent based on the total monomer charge. It is preferred to use polyethylene having a density at 25 C. of 0.950 to 0.980 gram per cubic centimeter.

The preferred method of making the polymer or copolymer is that described in the patent to Hogan et al., US. 2,825,721. Other methods can be used, for example low pressure methods employing organometallic catalyst systems are suitable. An example of such a process is the polymerization of ethylene in a hydrocarbon diluent in the presence of a mixture of triethylaluminum and titanium tetrachloride as the catalyst system. The temperature can be from room temperature up to about 300 C. with a pressure sufficient to maintain a liquid phase.

It is recognized that certain polypropylene fibers can be woven into fabrics that have good dimensional stability, superior to similar polyethylene fibers in this re spect. In order to compare the surface, frictional properties of fibers of polyethylene and polypropylene the following test was devised:

A segment of pipe 2 inches in diameter formed from polyethylene having a density of 0.960 gram per cubic centimeter and prepared according to the above-mentioned method of Hogan et al. was clamped in a horizontal position. To each end of the fiber to be tested was attached a small bucket, the two buckets being adjusted to the same weight. The fiber was then suspended over the horizontal pipe and shot was added to one bucket until downward movement was initiated and maintained at a uniform rate. The difference in weight between the buckets was then determined and recorded as a measure of frictional resistance between the fiber and the surface of the polyethylene pipe.

A fiber 6 mils in diameter drawn from polyethylene prepared by the method or Hogan et al. and having a density at 25 C. of 0.959 Was tested according to the above procedure and weight differential of 25 grams was required. A 6 mil fiber of 100 percent isotactic polypropylene, a material having a cocfiicient of friction in a desirable range for textile manufacture, was tested in the same manner and a weight differential of 35 grains was required.

As measured by the above described procedure it is desired to increase the frictional resistance of the ethylene polymer fiber at least about 20 percent in order to improve substantially the character of the fiber as a textile material. Increases considerably in excess of this can be obtained by the treatment of my invention and it will be the decision of each fabricator as to how high an increase in frictional resistance is required for a given purpose. Since the threads of lower denier can form a tighter weave, the cumulative effect of a given increase in frictional resistance will be correspondingly greater. Radical increases in frictional resistance, for example to percent or more, are obtained at a sacrifice in tensile strength. This is not a problem especially for most applications because of the tremendous range of tensile strengths possible with these fibers. It thus becomes a simple choice to select a fiber of the correct tensile strength for treatment in order that the resulting material will have the desired properties both in tensile strength and surface coefficient of friction.

Fibers, especially the monofilaments used in my invention, have a diameter of 0.01 to 100 mils, and more usually about 0.1 to 50 mils. The tensile strength of these fibers cold drawn is above about 30,000 p.s.i., frequently about 90,000 to 100,000 p.s.i., and can range as high as 150,000 to 250,000 p.s.i., measured at a temperature in the range of 18.3 to 37.8 C. Spun threads,

can be knotted more securely than can the untreated material.

The solvent used in this treatment should be a hydrocarbon, preferably one which boils above the temperature of the contacting process. Broadly any hydrocarbon solvent having 3 to 12 carbon atoms per molecule is suitable; however, elevated pressures would be re quired to maintain the lower boiling materials in the liquid phase. Preferably the solvent has at least 6 carbon atoms per molecule. Examples of suitable solvents are hexane, cyclohexane, benzene, toluene, xylene, cumene, cymene, decalin, tetralin, and the like. It is desirable to operate at atmospheric pressure to avoid mechanical problems.

Reference is now made to the drawing which illustrates how the treatment of my invention can be integrated in the production line of a fiber drawing operation. Molten polymer is forced from extruder 10 through die 11 forming a strand 12. This strand is quenched in water bath 13 which is maintained at about 24 C. The quenched filament passes from bath 13, over roll 14 and into drawing bath 16. The temperature for cold drawing high density polyethylene is preferably in the range of 38 to 127 C. The temperature is maintained by passing the filament through a bath of polyhydric alco hol such as glycerol while stretching the filament to to times its original length. The filament is now drawn down to its desired size and passes from bath 16, over rollers 17 and 18 and into bath 19 for pre-shrinking. This is an optional step which reduces the tendency of the fiber to shrink later on in use. The pre-shrinking bath can be water or a polyhydric alcohol inert to the polyethylene. The temperature of bath 19 is 71 to 127 C. and the fiber is passed through a sufficient number of loops to be retained in this bath for a sufiicient length of time to achieve the desired result. In certain instances adequate pre-shrinking can be obtained in 0.5 to 5 secends, and if desired this step can be omitted as a separate operation and pre-shrinking allowed to occur during the solvent treating step of my invention.

The filament next passes over rolls 20 and 21 and into the solvent bath 22 for treatment according to my invention. The residence time of the filament in bath 22 is extremely short, a matter of only 0.05 to 10 seconds. It should be understood that the relative sizes of the respective baths and the lengths of immersed filament as shown in the drawing is no indication of residence time. The drawing is purely schematic in this respect.

The filament passes around rolls 23, 24, 26 and 27 in bath 22. Residence time in bath 22 can be varied by the relative positions of rolls 24 and 26. Any other suitable arrangement which will permit the filament to pass rapidly into and out of the solvent can be substituted for that illustrated. Upon leaving the bath 22 the filament 12 is dried by a blast of warm air from dryer 28 and wrapped on spool 29 for storage until use.

The temperature of the solvent bath must be at least 100 C. for below this temperature there is no significant alteration of the fibers surface within a practical residence time. Preferably the solvent bath is at least 110 C. It is not desirable to have the solvent hotter than 125 C. as above this temperature it is too difficult to avoid deterioration of the filament. A preferred temperature range is from 110 C. to 120" C.

Within the operative temperatures of 100 to 125 0., residence times of 0.05 to 10 seconds can be used, matching the shorter residence times with the higher temperatures and vice versa. Of course care must be exercised not to dissolve the filament entirely but one operating within the prescribed limits can readily determine the proper temperature and residence time in order to confine the solvent action to the surface of the particular filament to be treated. Preferably the filaments are held in the solvent for 0.1 to 5 seconds. When they emerge from the bath and are dried the change in their surface is obvious from the appearance which has a soft luster.

A better understanding of my invention and appreciation of its advantages is provided by the following example.

A monifilament of polyethylene, 5.5 mils in diameter, was looped over a 2-inch polyethylene pipe wrapped with polyethylene (0.96 density, 0.9 melt index) film to provide a uniform surface. The polyethylene from which the filament was formed was prepared by the method of Hogan et al. and had a density of 25 C. of 0.959 gram per cubic centimeter, a melt index of 1.3, an Izod impact strength of 3.64 ft. lbs/in. (ASTM D-256), a tensile strength of 4520 p.s.i. and an elongation of 20% on a compression molded sample (ASTM D638-52T), and contained 0.019 percent Ionol as an antioxidant. To each end of the filament a 30gram cup was attached and sufiicient weight was added to one cup to induce uniform fall of 2 inches per second. This weight (about 30 g ams) was regarded as the zero condition and increases in frictional resistance of polyethylene fibers as a result of solvent immersion were measured from this value.

Several monofilaments of the same size and material as used for the control were immersed in commercial mixed xylenes at various temperatures and for various periods. These treated filaments were evaluated for frictional resistance by the same method and the increases in friction over the control are reported in the following table.

Frictional Resistance Weight Dilference Grains) Run No.

Residence Time, Sec.

Tensile strengths were determined by the method ASTM D-638-52T.

The above data demonstrate that the frictional resistance of a polyethylene fiber can be improved by solvent treatment without destroying its tensile strength. It is further shown that the temperature of the solvent is critical since the C. treatment was completely ineffective, even with a 5 minute residence time.

In density determinations the specimens should be prepared by compression molding the polymer at 171 C. until completely molten followed by cooling 93 C. at a rate of about 5.6 C. per minute. Water is then circulated through the mold jacket to continue the cooling to 66 C. at a rate not exceeding 11.1 C. per minute. The polymer is then removed from the mold and cooled to room temperature.

Density was determined by placing a smooth, void-free pea-sized specimen cut from a compression molded slab of the polymer in a 50-ml., glass-stoppercd graduate. Carbon tetrachloride and methyl cyclohexane were added to the graduate from burettes in proportion such that the specimen is suspended in the solution. During the addition of the liquids the graduate is shaken to secure thorough mixing. When the mixture just suspends the specimen, a portion of the liquid is transferred to a small test tube and placed on the platform of a Westphal balance and the glass bob lowered therein. With the tem perature shown by the thermometer in the bob in the range 22.8 to 256 C. the balance is adjusted until the pointer is at zero. The value shown on the scale is taken as the specific gravity. With the balance standardized to read 1.000 with a sample of distilled water at 4 C. the specific gravity will be numerically equal to density in grams per cc.

Melt index was determined according to ASTM D1238-52T using 5 samples at 2 minute intervals, averaging the 5 values (weights), discarding any values which deviate from the average by more than 5 percent (by weight), reaveraging and multiplying by 5 to obtain the amount of polymer extruded in minutes.

As will be evident to those skilled in the art various modifications can be made in my invention without departing from the spirit or scope thereof.

I claim:

1. A method of treating a filamentous article of ethylene polymer having a density at 25 C. of 0.940 to 1.00 gram per cubic centimeter which comprises immersing said article in liquid hydrocarbon solvent at 100 to 125 C. and withdrawing said article from said solvent after a residence time of 0.05 to 10 seconds.

2. The method of claim 1 wherein said ethylene polymer is a polymerizate of a monomer system containing ethylene and up to 30 weight percent monoolefin having 3 to 4 carbon atoms per molecule.

3. The method of claim 2 wherein said ethylene polymer is polyethylene.

4. The method of claim 1 wherein said solvent has 3 to 12 atoms per molecule.

5. A method of improving a polyethylene fiber for textile manufacture which comprises passing said fiber through a bath of liquid hydrocarbon solvent having 6 to 12 carbon atoms per molecule at 100 to 125 C. so that the residence time of said fiber in said solvent is 0.05 to 10 seconds, said polyethylene having a density at 25 C. to 0.940 to 1.00 gram per cubic centimeter.

6. A method of improving for textile manufacture a polyethylene fiber having a diameter of 0.01 to 100 mils and a tensile strength of 30,000 to 250,000 p.s.i. at a temperature of 18.3 to 37.8 C., said polyethylene having a density of 0.950 to 0.980 gram per cubic centimeter 6 at 25 C. which comprises passing said fiber into iiquid hydrocarbon solvent having 6 to 12 carbon atoms per molecule at a temperature of to C. and withdrawing said fiber from said solvent within 0.1 to 5 seconds so that the action of said solvent is confined to the surface of said fiber.

7. A filamentous article of ethylene polymer having a density at 25 C. of 0.940 to 1.00 gram per cubic centimeter and a frictional resistance of from 20 to 100 percent greater than an untreated article having the same composition and density.

8. The article of claim 7 wherein said article is a monoiilarnent.

9. The article of claim 7 wherein said article is a multifilament strand.

10. A polyethylene fiber having a diameter of 0.01 to 100 mils, a tensile strength of 30,000 to 250,000 p.s.i. at a temperature in the range of 18.3 to 37.8 C., a den sity of 0.95 to 0.98 at 25 C. and a frictional resistance of from 20 to 100 percent greater than an untreated fiber having the same composition, diameter, tensile strength and density.

11. A textile material woven from the fiber of claim References Cited in the fiie of this patent UNITED STATES PA iENTS 2,198,927 Waterman et a1. Apr. 30, 1940 2,325,060 Ingersoil July 27, 1943 2,367,173 Martin Jan. 9, 1945 2,889,611 Bedell June 9, 1959 2,973,242 Jurgeleit Feb. 28, 1961 FOREIGN PATENTS 204,680 Austria Aug. 10, 1959 

1. A METHOD OF TREATING A FILAMENTOUS ARTICLE OF ETHYLENE POLYMER HAVING A DENSITY AT 25*C. OF 0.940 TO 1.00 GRAM PER CUBIC CENTIMETER WHICH COMPRISES IMMERSING SAID ARTICLES IN LIQUID HYDROCARBON SOLVENT AT 100 TO 125* C. AND WITHDRAWING SAID ARTICLE FROM SAID SOLVENT AFTER A RESIDENCE TIME OF 0.05 TO 10 SECONDS.
 7. A FILAMENTOUS ARTICLE OF ETHYLENE POLYMER HAVING A DENSITY AT 25*C. OF 0.940 TO 1.00 GRAM PER CUBIC CENTIMETER AND A FRICTIONAL RESISTANCE OF FROM 20 TO 100 PERCENT GREATER THAN AN UNTREATED ARTICLE HAVING THE SAME COMPOSITION AND DENSITY. 